Physical inactivity is an independent risk factor for cardiovascular disease, and is linked to obesity and early onset Type II diabetes in children. Self-report is the most common method of collecting physical activity data, yet there is a paucity of research about self-report methods that support valid recall in children. Child energy expenditure in physical activity is being determined1, but these data have not been integrated into self-report instruments. This study will design with children, implement and evaluate a web- based computer application for child self-report of physical activity. Included will be algorithms to calculate child energy expenditure and feedback mechanisms for children, parents, and health care professionals. First a qualitative research design will be used to determine what children consider a "friendly" computer interface. This information will provide the basis for interface development. The second phase will pilot the application to examine children's use of the program to self-report their activities. The final study phase will be a validation study with corresponding physiologic measurements. Capitalizing on available computer technology will facilitate data collection speed and accuracy and provide a mechanism for feedback. Both child energy expenditure data and computer software for self-reporting can be applicable to other populations.